The cold slivers that remain are disintegrating so fast that scientists estimate the park will have no glaciers in 30 years.

Boulder Glacier, once massive enough to contain a human-dwarfing ice cave, was gone by 1998. Grinnell Glacier, beloved by tourists and scientists alike, has lost 90 percent of its volume since 1850.

The dwindling glaciers amid the deeply chiseled landscape of this national park offer the clearest and most visible sign of climate change in America. It is an omen even a child can grasp in an instant: Ice that has lasted in these high alpine valleys since the end of the Stone Age will soon vanish.

''It's not just going to happen in my lifetime,'' said Dan Fagre, a 49-year-old ecologist who leads the U.S. Geological Survey team working to chronicle climate change here. ''It's going to happen during my career.''

The unexpected speed of the demise of the glaciers has left scientists racing against time. They have only decades left -- nothing at all in geological time -- before they disappear.

''The scariest thing to me is realizing how fast these things are happening,'' said Blase Reardon, 39, an avalanche expert who has worked in the park for the last two years. ''Being here is like having a front row seat at the Indianapolis 500.''

The melting here is being mimicked around the world, from the snows of Mount Kilimanjaro in Tanzania to the ice fields beneath Mount Everest in the Himalayas. Experts predict that glaciers in the high Andes, the Swiss Alps and even Iceland could disappear in coming decades as well.

In contrast to these more remote, high-altitude areas, the accessibility of Glacier gives scientists a chance to get the most intimate view possible of a dying glacier.

Since 1991, a team of scientists has measured the most ephemeral details of the glaciers. They have analyzed the cycles of precipitation and temperature. They have dragged ground-penetrating radar over crevasses and risked skiing into avalanches to measure snowfall. They have analyzed soil carbon and counted frog eggs to document the unique ecology of glaciers and their meltwater streams.

But for all the gigabytes of data team members have accumulated, they realize they have only scratched the surface. The transformation of the park has turned out to be far more complex than anyone imagined. For example, even as most glaciers here race toward extinction, a handful seem to effortlessly maintain their grip on mountain peaks.

''It makes you question what you know,'' said Fagre, ''which is the real point of science.''

While the team has spent much of its tenure here talking about streamflow data, snowfall records and vegetation dynamics, they have started talking about something new: the loss of beauty. These scientists know they are recording the last vestiges of a world that may soon exist only in their computers, photographs and memories -- a world their grandchildren may never see.

''When the permanent parts of the landscape start disappearing, that's unsettling,'' said Fagre, who has lived and worked in the park for more than a decade. ''It's still a beautiful mountain, but without glaciers, an identity is lost.''

To glaciologists who thrill to see the groaning dynamics of ice in real time, there still is beauty in the rocky new landscapes. Glaciers often drip away into milky lakes of ''unusual, gorgeous, turquoise, practically indescribable color,'' said Jeffrey Kargel, a USGS scientist who monitors many of the world's wasting glaciers from space. The color is a product of light reflecting off ''glacial flour,'' or ground-up rock that floats in meltwater.

The terrain left behind by a retreating glacier is like land recovering from fire, Kargel said. It may look devastated, scarred and littered with boulders. But soon, lichens, grasses and wildflowers grow. Those who stand at the edge of retreating glaciers are likely standing where no human has stood before. ''It's not all doom and gloom,'' Kargel said.

Some of this epochal change can be hard to detect, particularly for those who have spent much of their lives in the park. But pictures can overwhelm.

In most areas with vanishing glaciers, there are few historical records documenting how the ice has responded to the warming of the planet during the last century -- or even the last decade. Here, an archive of 12,000 photos offers an unparalleled window into the last century.

The creation of this park, the nation's 10th, neatly coincides with the rise of photography. Boxes of photos of the park date back to the 19th century, and can be compared with modern photographs taken from the same locations.

Of 17 glaciers that have been rephotographed, said Karen Holzer, a USGS scientist, four small ones in the park's shadiest, north-facing recesses have not changed at all. Twelve have shrunk considerably. And one, Boulder, disappeared.

A set of photos of Grinnell Glacier through time now hangs in the park's Apgar visitor center. The images startle visitors who think of climate change only as some distant, far-off threat.

Glaciers take decades to respond to warming. Scientists say the melting of the glaciers seen today is largely because of leftover warming from the end of the Little Ice Age and global warming, the recent heating of our planet. Most scientists agree the recent warming is mainly a product of industrial activity.

For the first years of the study, the phenomena seemed a simple matter of rising temperatures melting the ice. But closer analysis of temperature data from nearby Kalispell didn't fit that picture. Annual temperatures there have not warmed significantly in the last century -- the time when glaciers have retreated most.

It is a world of unexplained contradiction and complexity that keeps Fagre going. As long as the glaciers last, he will keep teasing secrets from them, measuring their size and monitoring the lakes of milky aquamarine meltwater pooling beneath them. He will monitor the firs, track bull trout populations and use powerful computers to model new forest fire cycles.

There is some comfort in the long columns of data he can generate, some satisfaction in knowing the careful work could one day help reduce ecological damage from retreating glaciers around the world.

But as he hikes through the mountains, Fagre, the son of a theologian, cannot shake his sense of loss.

''I'm an ecologist who knows climate change is neither good nor bad,'' he said as he hiked across a ridge overlooking a set of classic U-shaped glacial valleys amid 10,000-foot peaks.